1. Field of the Invention
The present invention relates to magnetoresistive sensors and more particularly to a lead overlay sensor design that provides for reduced trackwidth size and improved trackwidth control.
2. Description of the Related Art
Digital memory lies at the heart of all computer systems. Magnetic Disk Drives provide the this memory function in most modern computers systems, due to their ability to inexpensively store large amounts of data in such a manner that the data can be immediately, randomly retrieved. A magnetic disk drive includes one or more rotating magnetic disks, magnetic write and read heads that are suspended by a suspension arm above the rotating disk and an actuator that swings the suspension arm to place the read and write heads over selected circular tracks on the rotating disk. The read and write heads are directly mounted on a slider that has an air bearing surface (ABS). The suspension arm biases the slider into contact with the surface of the disk when the disk is not rotating. When the disk rotates, viscous forces in the air cause the air immediately adjacent to the disk to move with the disk. The ABS is aerodynamically configured to allow the slider to fly upon this moving air immediately adjacent to the disk surface.
As the disk moves past the slider, the write head emits magnetic flux pulses in order to imprint a magnetic signal onto the disk. These magnetic signals can then be read by the read head by moving the slider over a desired track and reading the magnetic signal as it moves past the read head.
Various magnetic sensors have been used to read data from a magnetic medium. Some prior art disk drives have used anisotropic magnetoresistive (AMR) sensors, while more recently disk drive devices have employed giant magnetoresistive sensors (GMR) also known as spin valves. Various other sensors have been proposed as well, such as tunneling magnetoresistive sensors (TMR). At present, GMR sensors are by far the most widely used and as such will be described in more detail herein. GMR sensors operate on what has been called the “spin valve effect”, and includes a non-magnetic conductive spacer material sandwiched between layers of magnetic material. The layer at one side of the side of the spacer material has a magnetic moment that is pinned in a given direction, this layer is generally referred to as the pinned layer. The magnetic material at the other side of the spacer layer has a magnetization that is biased perpendicular to that of the pinned layer, but is free to rotate in the presence of a magnetic field. This layer is generally referred to as the free layer. The selective spin scattering of electrons passing through the sensor causes the electrical resistance of the sensor to change as the angle of the magnetization of the free layer relative to that of the pinned layer changes. In this way, as the moves passed a magnetic field produced by the passing magnetic disk, the angle of the free layer magnetization changes, thereby changing the resistance of the sensor. This change in resistance is detected by passing a sense current through the sensor and detecting the voltage change across the sensor.
The computer industry constantly requires larger memory storage capacity in ever smaller devices. One way to increase data storage efficiency is to reduce the width of a track of data. The reduction of track width allows more tracks of data to be stored on a single disk. One attempt to minimize track width can be more readily understood with reference to FIG. 1 which describes a read sensor 10 having a lead overlay design. The sensor 10 is built upon a gap layer 12, which is an electrically insulating, non-magnetic material. An antiferromagnetic material 14 is formed over the gap layer and is used to fix the magnetization of a magnetically pinned layer 16, in a manner which will be familiar to those skilled in the art. An electrically conductive, non-magnetic spacer layer 18 is formed over the pinned layer, and a magnetically free layer 20 is formed over the spacer layer 18 at the side opposite the pinned layer. Hard bias layers 24 are formed at either side of the sensor 10. The hard bias layers are constructed of a material having a high magnetic moment when magnetized acts to bias the magnetization of the free layer in a desired direction due to magnetostatic forces between the hard bias material 24 and the free layer 20. In the lead overlay design described herein, electrical leads 26 are formed over the top of the sensor 10 at portions of the sensor. The leads 26 provide the sense current to the sensor, and as will be appreciate by those skilled in the art, the track width TW of such a design is defined as the distance between the leads. Prior art lead overlay designs and methods of manufacture make accurate track width definitions somewhat difficult as will be described in greater detail below in a discussion of the prior art methods of making such lead overlay sensor.
With continued reference to FIG. 1, the hard bias material 22 tends to slightly overlap the free layer 20, resulting in what has been called a “birds beak” 26. Such a birds beak 26 is undesirable because it results in magnetic instability in the free layer.
With reference to FIGS. 2 through 4 an exemplary method of manufacturing such a lead overlay sensor 10 will be described. With reference to FIG. 2, a layer of sensor materials 28 is formed over the gap material 12. The layer of sensor material could include the various layer making up the sensor 10 as described with reference to FIG. 1 or could be layers making up some other type of sensor such as ARM, TMR etc. A first mask 30, which could be a bi-layer photoresist mask is formed over the sensor layer 28 and is formed of such a width as to define the edges of the sensor. An ion milling process indicated by arrows 32 is used to remove sensor material not protected by the mask 30. This process is generally referred to in the industry as the K2 milling process, or just K2. After the ion milling process 32 has been completed, the hard bias layers 22 are deposited, using the same mask 30 that was used to define the edges of the sensor 10. As can be seen with reference to FIG. 3, this method of construction allows the hard bias layers 22 to slightly overlap the sensor 10. After the hard bias 22 has been deposited, the first mask 30 is removed. The first mask 30 is replaced with a second mask 34, which is narrower than the first mask, and can also be constructed as a bi-layer photoresist structure. As will be seen, this second mask defines the track width dimension. With the second mask 34 in place, the lead material is deposited. As can be seen with reference to FIG. 4, since the second mask 34 is narrower, than the first mask 30, the lead material can be deposited directly onto the sensor at side portions of the sensor extending inward from the inner edges of the hard bias material 22. This step forming the second mask 34 and forming the leads 24 is referred to in the industry as “K5”. With the lead layer formed, the second mask layer 34 can be removed and a cap layer (not shown) can be deposited to protect the sensor from subsequent manufacturing process that will be familiar to those skilled in the art.
As will be appreciated from the above, the track width is defined by the second mask 34. However, as can be seen, this critical photolithographic step is performed on a surface having a severe topography rather than on planar surface as would be desired. This makes accurate photolithography difficult, and as a result makes accurate definition of the track width difficult. In addition, the thickness with which the leads can be deposited is limited, because depositing too much lead material would completely cover the resist structure 34 making it impossible to remove.
From the above it will be appreciated that there remains a need for a magnetic sensor design that provides for very accurate track width definition, while utilizing presently implemented manufacturing techniques. There also remains a need for a lead overlay design, and method of manufacture, that will minimize the effects of hard bias birds beaks.